It is common practice to form a transparent coating film having antistatic and anti-reflection capabilities on a surface of any of transparent substrates such as display panels of, for example, a cathode ray tube, a fluorescent character display tube and a liquid crystal display for the purpose of effecting the reductions of static electricity and reflection at such a surface.
Recently, attention has been drawn to the influence on human health of electromagnetic waves emitted from, for example, a cathode ray tube. Thus, it is desired to not only take the conventional antistatic and anti-reflection measures but also shield the above electromagnetic waves and the electromagnetic field produced by the emission of electromagnetic waves.
One method of shielding, for example, the above electromagnetic waves comprises forming a conductive coating film for shielding electromagnetic waves on a surface of a display panel of, for example, a cathode ray tube. However, although it is satisfactory for the conventional antistatic conductive coating films that the surface resistivity is at least about 10.sup.7 .OMEGA./.quadrature., the conductive coating film for electromagnetic shielding must have a surface resistivity as low as 10.sup.2 to 10.sup.4 .OMEGA./.quadrature.
When it is intended to form the above conductive coating film of low surface resistivity with the use of the conventional coating liquid containing a conductive oxide such as Sb doped tin oxide or Sn doped indium oxide, the thickness thereof must inevitably be larger than that of the conventional antistatic coating film. However, the anti-reflection effect can be exerted only when the thickness of the conductive coating film is in the range of about 10 to 200 nm. Therefore, the use of the conventional conductive oxide such as Sb doped tin oxide or Sn doped indium oxide involves such the problem that it is difficult to obtain a conductive coating film which has low surface resistivity and is excellent in electromagnetic shielding and anti-reflection properties.
Another method of forming a conductive coating film of low surface resistivity comprises applying a coating liquid for forming a conductive coating film which contains fine particles of a metal such as Ag to thereby form a coating film containing the fine metal particles on a substrate surface. In this method, a dispersion of colloidal fine metal particles in a polar solvent is used as the coating liquid for formation of a coating film which contains fine metal particles. In this coating liquid, the surface of fine metal particles is treated with an organic stabilizer such as polyvinyl alcohol, polyvinylpyrrolidone or gelatin in order to improve the dispersibility of the colloidal fine metal particles. However, the conductive coating film formed from the above coating liquid for formation of a coating film which contains fine metal particles has a drawback in that fine metal particles contact each other through the organic stabilizer in the coating film to thereby tend to have large interparticulate resistance with the result that the surface resistivity of the coating film cannot be low. Thus, it is needed to conduct heating at temperatures as high as about 400.degree. C. after the formation of the coating film to thereby decompose and remove the organic stabilizer. However, the heating at high temperatures for decomposition and removal of the organic stabilizer encounters the problem that fusion and aggregation of fine metal particles occur to thereby deteriorate the transparency and haze of the conductive coating film. Further, with respect to, for example, a cathode ray tube, the problem is encountered that quality deterioration is caused by exposure to high temperatures.
Moreover, the conventional transparent conductive coating film containing fine particles of a metal such as Ag involves the problem that the metal is oxidized, particulate growth is caused by ionization and occasionally corrosion occurs with the result that the conductivity and light transmittance of the coating film are deteriorated to thereby lower the reliability of the display device.
An object of the present invention is to resolve the above problems of the prior art and to provide a coating liquid for forming a transparent conductive coating which has surface resistivity as low as about 10.sup.2 to 10.sup.4 .OMEGA./.quadrature.. and is excellent not only in antistatic, anti-reflection and electromagnetic shielding properties but also in reliability, a substrate having such an excellent transparent conductive coating, a process for producing the same and a display device including the above substrate with transparent conductive coating.